Discharge indicator tube



M r h 22, 19 HARUHIRO KOBAYASHI 3,242,378

DISCHARGE INDICATOR TUBE Filed June 12, 1962 2 Sheets-Sheet 1 INVENTOR H. KOBAYASHI by QZM AGENT March 22, 1966 HARUHIRO KOBAYASHI 3,242,378

DISCHARGE INDICATOR TUBE Filed June 12, 1962 2 Sheets-Sheet 2 (m) 1mm 200w mun/0 [L 5 ff ,3 in I 0 R -/0 -5 0 g CRITICAL CONTROL ELECWODE V0174 E a 8 40 :o a 2 H l NV E N TOR I-I KO BAYAS l-H by gmwyfww AG E NT United States Patent Ofiice Patented Mar. 22, 1966 3,242,378 DISCHARGE INDICATOR TUBE Haruhiro Kobayashi, Tokyo, Japan, assignor to international Standard Electric Corporation, New York, N.Y., a corporation of Delaware Filed June 12, 1962, Ser. No. 201,967 Claims priority, application Japan, June 26, 1961, 36/22,821 6 Claims. (Cl. CHE-84.6)

This invention relates to a cold cathode indicator tube, and particularly to a tube of this type which may be utilized in conjunction with low voltage, low current counting circuits.

The recent advances in electronics have led to the advent of small dimensioned counting circuits of low power consumption. This has resulted in counters with insufiicient power to directly ignite conventional indicator tubes, or neon lamps, so that the counting results may be visual- 1y displayed. intervening high voltage circuits may, of course, be employed, but these prove to be a costly addition.

Although there have been improvements in the indicator tube art (see, for example, Philips Technical Review, vol. 21, 195960, pp. 267275), these developments still lag the general state of the art; and at least 50 p.21. at v. are still required for tube operation. Furthermore, even the proposed tubes have statistical irregularities in darkness which result in inoperativeness under poor environmental conditions. The solution to this problem has proved vexing since the employement of a high anode voltage would introduce a poor degree of stability, which might produce a discharge upon the receipt of even minute noise.

It is, therefore, the object of this invention to provide a cold cathode discharge tube operable with a signal input of the order of I a.

It is a further object of this invention to provide such a tube which has operational stability in darkness.

The invention is promulgated upon what is termed a keep-alive discharge maintained on the surface of a cathode assembly which is opposite that upon which the display is intended.

Holes are bored through the cathodes to permit the diffusion therethrough of charged particles, produced by the keep-alive discharge, into the main discharge gap between the anode and the cathode assembly. Control electrodes disposed adjacent the holes produce an ion sheath, the thickness of which is regulated by the control electrode voltage so that the quantity of the charged particles diffusing into the main gap may be regulated. When the quantity of diffusing particles reaches a definite value, a discharge across the main gap is initiated, with the result that the desired cathode displays a neon glow. Inasmuch as the ion current which flows through the control electrode is very small, the discharge indicator tube can operate with an extremely small signal input. In addition the diffusion of the charged particles into the main gap allows the anode starting voltage to be decreased by the order of 100 volts With the result that a considerable fluctuation of the supply voltage to the anode does not affect stability. Furthermore, it is obvious that the keepalive discharge obviates the problem of darkness.

The above mentioned and other features and objects of this invention and the manner of attaining them will become more apparent and the invention, itself, will best be understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings wherein:

FIG. 1 shows schematically a side view of one embodiment of the invention together with the operating circuit therefor.

FIGS. 2, 3, and 4 are individual illustrations for the cathode assembly, anode, and keep-alive cathode, respectively, of the discharge tube of FIG. 1.

FIG. 5 is a graphic representation of the trigger characteristics of the discharge tube for a keep-alive current Of 50 ,ua.

FIG. 6 illustrates the curve of the control electrode current just prior to the initiation of anode breakdown.

Turning now to FIG. 1, the general electrode arrangement may be seen within the gas-filled, sealed envelope 15 (the gas is, for example, neon to which a small percentage of argon is added). The arrangement consists of an annular metal anode 1 of, for example, nickel or nichrome; ten plane cathodes 3 disposed radially and symmetrically about the axis; ten sets of keep-alive cathodes 4 disposed on the opposite sides of the holes with respect to the anode; and ten control electrodes 2 disposed on the anode side. From the above number of elements within each elemental group, it is obvious that a decade indicator has been chosen for the example.

The cathode structure, seen in FIG. 2, is a molybdenum ring, the face of which is sector coated with insulation 18. The ten sectors 3 each act as a cathode, and contain a hole 5 therethrough for the diffusion. The additional cathode structure, having the function of maintaining the discharge, consists of ten keep-alive cathodes 4 (FIG. 4) Welded to an annular ring 16 of nickel or molybdenum. The ten control electrodes or triggers 2 are wires disposed like radial spokes on an imaginary wheel, each spoke being insulated from its neighbor, and appearing in proximity to one of the holes 5.

The attendant circuitry shown in FIG. 1 illustrates only two sets of trigger connections. It will be understood, however, that ten such connections through additional resistors 13 and counting circuit outputs, exist.

The main cathodes 3 are grounded while the keep-alive cathodes are supplied, through a common resistor 14, with a negative supply voltage obtained by rectifying (with rectifier 11 and filter 12) the alternating-current voltage of transformer 8. By setting the negative voltage and the series resistors within a suitable range, a glow discharge can be induced between the ten keep-alive cathodes and the ten cathodes. A portion of the electrons and ions produced by the glow discharge diffuse through the holes 5 into the space on the anode side. A negative bias voltage applied by a source 9 to the control electrodes 2 provide ion sheaths around the holes. By adjusting the bias voltage so that the ion sheaths clog the holes, it is possible to prevent the charged particles from reaching the main gap on the anode side. The application of an input signal 19 to the desired control electrode 2, will then raise the potential thereof so that the consequent decreased thickness of the ion sheath eventually forms a split between the sheath and the cooperating hole 5 and allows the diifusion of charged particles into the main gap. The predetermined anode voltage present (by virtue of transformer 8, a rectifier 7, and resistor 6) will therefore cause an electron avalanche to initiate the breakdown, and the vivid and specific radiation of the sealed gas on the cathode surface facing the selected control electrode.

FIG. 5 shows the relation between the critical anode voltage V taken as the ordinate, and the critical control electrode voltage V taken as the abscissa, for a discharge indicator tube according to the invention. The tube is filled with neon gas mixed with 5% argon at mm. Hg, and has a keep-alive cathode current of 50 ta. Inas much as the cathodes are spaced by the insulated layer portions 18, the discharge produced at one cathode is prevented from spreading to its neighbor and only that cathode to which the signal is applied glows in the main discharge gap. The input current required is equal to the control electrode current flowing just before ignition. FIG. 6 shows the values obtained for the control electrode current versus the control electrode voltage V in the case of a floating anode. From the curve it may be seen that an input current of less than l ra. is suflicient. Inasmuch as a keep-alive cathode current of 1,148.. corresponds to a flow of 6.25 10 electrons or ions per second, the probability of a mis-operation in darkness is remote. It is important to note that by virtue of the half-wave-rectified voltage applied to the anode, the withdrawal of the input signal extinguishes in turn the main discharge so that the tube is prepared for the application of the succeeding signal.

Although only a specific embodiment of the invention has been explained in the foregoing, it is to be noted that the cathodes may be in the shape of numerals or alternatively the anode may have numeral slits so that a shaped glow will result. The anode may be supplied with a direct smooth voltage, which value is in the range between the anode sustaining voltage and the maximum anode voltage without self ignition so that the tube, once operated, may be reset by the application of a negative pulse to the anode.

In addition, it is to be understood that the tube and elements are not restricted to circular form or decade indication; and that this description is made only by way of example and not as a limitation upon the scope of my invention as set forth in the objects and accompanying claims.

What is claimed is:

1. A cold cathode gas filled discharge tube comprising an anode; at least one cathode, having an aperture therethrough, disposed in facting relation to said anode and forming therewith a main discharge gap; means for supplying different bias potentials to said anode and cathode; at least one keep-alive cathode, disposed in proximity to said aperture on the side opposite said anode, defining with said first mentioned cathode an auxiliary keep-alive discharge gap; means for supplying a voltage to said keep-alive cathode which is sufficiently more negative than the bias voltage on said cathode to create a glow discharge between said cathodes, and at least one control electrode disposed adjacent said aperture in the main discharge gap; means, including a source of input pulses for supplying said control electrodes with voltages for controlling the diffusion of charge particles into said main gap.

2. A cold cathode gas filled discharge indicator tube for a decade counting circuit comprising an anode; ten electrically connected substantially fiat cathodes each disposed in facing relation to a portion of said anode and forming therewith ten main discharge gaps, each of said cathodes having an aperture therethrough; means for supplying bias voltages to said anode and each of said cathodes ten electrically connected keep-alive cathodes each disposed in proximity to one cathode aperture on the side opposite said anode, defining with said first mentioned cathodes ten auxiliary keep-alive discharge gaps; means for supplying to each of said keepalive cathodes a voltage which is more negative than the voltage on said cathode and which is sufficient to create a glow discharge between said cathode and each of said keep-alive cathodes; and ten control electrodes each disposed adjacent one aperture in the corresponding main discharge gap; means, including a signal input pulse source for supplying each of said control electrodes with a variable voltage for controlling the diffusion of charged particles into that gap.

3. A cold cathode gas filled discharge indicator tube fod a decade counting circuit comprising a circular anode; ten electrically connected substantially fiat cathodes disposed in a circular array, each cathode disposed in facing relation to a sector of said anode and forming therewith ten main discharge gaps, each of said cathodes having an aperture therethrough; means for supplying difierent bias voltages to said anode and each of said cathodes; an annular metal ring having ten axially directed metal fingers mounted thereon, said ring being disposed on the side of said cathode opposite said anode, the unmounted end of each of said fiingers being in proximity to each of said apertures on one-to-one basis and defining with said cathodes ten keep-alive discharge gaps; means for supplying a voltage to said ring which is more negative than the voltage on each of said cathodes and which is suflicient to create a glow discharge between each of said fingers and the corresponding cathode; and ten radially disposed control electrodes each in a main discharge gap adjacent a cathode aperture; means, including a signal input pulse source for supplying each control electrode with a variable voltage for controlling the dilfusion of charged particles into the corresponding gap.

4. .In a method for operating a cold cathode gas filled discharge tube having: an anode; a cathode spaced from and facing said anode and having an aperture therethrough; at least one electrode positioned between said anode and cathode and adjacent said aperture; and at least one keep-alive electrode disposed on the side of said cath ode opposite said anode and in close proximity of said aperture, the combination of steps comprising: supplying predetermined different bias potentials to said anode and cathode; creating a glow discharge between said cathode and said keep-alive electrode by applying a voltage to said keep-alive electrode which is more negative than said cathode bias voltage; preventing ion flow through said aperture during preselected intervals by applying a negative voltage to said control electrode which is sufiicient to create an ion shield around said aperture; and varying the potential supplied to the control electrode to alter said shield to permit ion fiow through said aperture.

5. In the method of claim 4 the additional steps of forming said cathode to be a segmented ring having the segments thereof separated by insulating material and providing each cathode segment with an aperture therethrough.

6. In a method as set forth in claim 5, the additional steps of: providing one control electrode and one keepalive electrode for each aperture; and supplying the control electrode with a bias voltage which is sufficient to create an ion shield in the vicinity of said aperture to prevent ion movement therethrough; and supplying control input pulses to said control electrode to increase the potential thereof by an amount sufficient to decrease said ion shield to permit ions to flow into the gap between said anode and cathode.

References Cited by the Examiner UNITED STATES PATENTS 2,295,569 9/1942 Depp 313-197 2,575,372 11/1951 Townsend 315--84.6 2,928,013 3/1960 Gawehn 313197 X DAVID J. GALVIN, Primary Examiner. 

1. A COLD CATHODE GAS FILLED DISCHARGE TUBE COMPRISING AN ANODE; AT LEAST ONE CATHODE, HAVING AN APERTURE THERETHROUGH, DISPOSED IN FACTING RELATION TO SAID ANODE AND FORMING THEREWITH A MAIN DISCHARGE GAP; MEANS FOR SUPPLYING DIFFERENT BIAS POTENTIALS TO SAID ANODE AND CATHODE; AT LEAST ONE KEEP-ALIVE CATHODE, DISPOSED IN PROXIMITY OF SAID APERTURE ON THE SIDE OPPOSITE SAID ANODE, DEFINING WITH SAID FIRST MENTIONED CATHODE AN AUXILIARY KEEP-ALIVE DISCHARGE GAP; MEANS FOR SUPPLYING A VOLTAGE TO SAID KEEP-ALIVE CATHODE WHICH IS SUFFICIENTLY MORE NEGATIVE THAN THE BIAS VOLTAGE ON SAID CATHODE TO CREATE A GLOW DISCHARGE BETWEEN SAID CATHODES, AND AT LEAST ONE CONTROL ELECTRODE DISPOSED ADJACENT SAID APERTURE IN THE MAIN DISCHARGE GAP; MEANS INCLUDING A SOURCE OF INPUT PULSES FOR SUPPLYING SAID CONTROL ELECTRODES WITH VOLTAGES FOR CONTROLLING THE DIFFUSION OF CHARGE PARTICLES INTO SAID MAIN GAP. 